A. Field of the Invention
The present invention generally relates to elongated plastic members formed by extrusion, and particularly relates to reinforced plastic marine pilings.
B. Discussion of the Related Art
Traditional marine pilings are made of steel, concrete, or wood. Steel and concrete are very heavy and expensive and do not have desired resiliency for fendering applications. Steel is especially subject to rapid corrosion in a marine environment. Wood suffers from rapid erosion and is subject to attack by marine boring animals which deplete its effectiveness. In order to prolong its useful life, wood is typically treated with a preservative, such as creosote. However, creosote and other preservatives are detrimental to the environment. Furthermore, given the recent efforts for preservation of forests, the use of wood pilings is not desirable.
Pilings made of plastic have been proposed. For example, U.S. Pat. No. 5,051,285 to Borzakian discloses a structural plastic member suitable for use as a plastic piling. A steel pipe is positioned in a mold and coated with thermoplastic resins, fillers, and additives. The plastic is cooled and the resultant plastic member is then removed from the mold.
This approach suffers many disadvantages. Marine pilings typically vary in length from ten to eighty feet and diameter as small as three inches depending on a specific application. As a result, a piling manufacturer must either construct molds of varying sizes, which is very expensive, or use a single mold to produce pilings of a certain length and diameter and join multiple pilings longitudinally to achieve the desired length.
The use of a mold also limits the length of a piling which can be produced. The plastic in the mold must be in a flowable state throughout the entire process of filling the mold. The flowable state becomes difficult to maintain as the length and size of the structure is increased. Additionally, the adhesion of the plastic to the pipe is difficult to control in such an operation where the plastic melt is introduced at one end of an elongated mold and required to stick to the metal core pipe at the opposite end, which is typically at least ten feet away. It is believed that such a formed structure would contain hollows or at least weak areas formed by interfaces between melt streams of different relative ages.
Because the length of the member is limited by mold size, the structure disclosed in Borzakian must be connected to other such structures to form pilings of the length required for a given application. Such joining methods and means are expensive, cumbersome and leave potential seams for water and other environmental factors to attack the metal pipe core.
Regardless of the production method, plastic pilings must be properly cooled so that the plastic maintains its appropriate shape. Such a cooling process may be lengthy, particularly since pilings typically exceed 10 inches in diameter and 30 feet in height. If cooling time is sacrificed, the piling may bend or sag from its desired shape.
Accordingly, there is a need for a piling structure that is corrosion resistant or corrosion proof, impervious to marine life, has desirable structural integrity and resiliency/toughness under side impact, is environmentally safe, and preserves natural resources. There is also a need for a process for making a piling structure that can produce pilings of a desired size without requiring multiple molds of varying sizes or the lengthwise coupling of several piling sections, and can properly and efficiently cool the piling while maintaining the desired shape.